Polyester fibers can be applied in clothing, decoration, and the like because of the advantages of their good abrasion resistance and low cost. Polyester fibers are of great importance in the application of synthetic fiber products. There are many varieties of polyester fibers, in which polyalkylene terephthalate formed by reacting terephthalic acid or its alkyl ester with alkanediol is widely used in many applications. The well-known polyalkylene terephthalate fibers include polyethylene terephthalate fibers (PET), polypropylene terephthalate fibers (PPT), and polybutylene terephthalate (PBT) fibers. Among them, polyethylene terephthalate fibers have about twice the strength as cotton and about four times the strength as wool, have elastic properties close to wool, and have excellent abrasion, crease, and heat resistance, as well as thermal stability. Consequently, PET fibers have become the most widely used synthetic fibers.
Polyethylene terephthalate fibers can be blended with other natural fibers such as wool and cotton to produce textile fibers with enhanced strength and durability. These combined fibers retain not only the physical properties of the polyesters, but also the desired qualities of the natural fibers. In general, when producing such a synthetic fiber, the formed polyester is extruded and drawn into linear filaments, and then stranded, curled, and chemically treated to obtain synthetic fibers having better properties than natural fibers such as wool and cotton.
In many applications, it is desirable that the textile fabric be available in a variety of colors, these colors being obtained by dyeing. However, unimproved polyethylene terephthalate fibers are not as stainable as most natural fibers, and must be dyed under the special conditions of high temperature, high pressure or both, or at normal atmospheric conditions using a dye carrier. Establishing these special conditions increases production costs as well as the investment in facilities. Furthermore, natural fibers such as wool, cotton, and spandex are thermally sensitive fibers, is which can cause problems when polyethylene terephthalate fibers are blended with these thermally sensitive fibers and dyed. As a result, the use of polyethylene terephthalate fibers is typically limited to specific applications, otherwise manufacturing complexity and costs increase in order to achieve the requirements of blending and dyeing.
In addition, there exist many disadvantages when fiber dyeability is improved by the physical and chemical reaction of dye carriers with the polyester fibers. Many dye carriers have functional groups that can chemically react with dye molecules and polyester fibers. These functional groups include carboxylic acids (particularly dicarboxylic or other multifunctional acids), organometallic sulfate or sulfonate compounds and the like. Reactive dyes can replace the disperse dyes in the above dyeing process, but this substitution can cause an increase in the production costs. Furthermore, these dye carriers will remain in the waste water and textile fabric after being processed, which poses risks to the environment.
In order to improve the dyeability of polyethylene terephthalate fibers, researchers have developed modified polyethylene terephthalate fibers to broaden the application fields of polyethylene terephthalate fibers without generating environmental pollution. U.S. Pat. No. 5,916,677 discloses 2-methyl-1,3-propanediol modified polyethylene terephthalate fibers having improved dyeability, elongation and fiber strength. However, the modified polyester fibers disclosed in that patent show poor colorfastness to laundering, can be easily dyed, and the dye therein can be easily washed out at the same time. As a result, these modified polyester fibers are also restricted to limited uses. U.S. Pat. No. 6,187,900 discloses a polyester fiber with easy dyeability at low temperatures, wherein the polyester fiber contains polypropylene terephthalate/polyethylene terephthalate (PPT/PET) copolyester. Although the formed polyester fiber of easy dyeability at low temperatures disclosed by that patent can decrease dyeing costs, the raw material “1,3-propanediol” for producing polypropylene terephthalate is not easily prepared. Consequently, 1,3-propanediol is in short supply and the price is high, which makes it difficult to reduce the total cost of production. Therefore, a modified polyester fiber is still needed that can undergo dyeing at low temperatures without increasing production costs.